Love is in the air

It may have become clear by now that our immune system plays an important part in many aspects of human biology. From the defence against pathogens to cancer therapies. Recently it has been suggested that it also influences partner choice.

The key players in this mechanism are the major histocompatibility complexes (MHC for short) These proteins are used to warn the so-called ‘antigen presenting cells’. The MHCs recognize a foreign protein (e.g., part of a virus), and present it to immune cells in order to start a specific immune response against that one pathogen. Kind of like a SWAT team entering a building to eliminate a target.

There are two different classes of these MHCs, type I and II. These classes each contain 3 different genes: HLA-A, HLA-B, HLA-C for the type I and HLA-DP, HLA-DQ and HLA-DR for type II. Each of these has many possible variants, so that every person has their own individual set of MHC types. This individual set is called a genotype.

The important thing to know about these MHCs is, that each variant has its own speciality. For example, one will be good at recognizing malaria, giving that person a better chance at combatting malaria. Whereas another person might have an MHC that protects them against HIV infection. So depending on which variant you get, you’ll be well protected against certain diseases, but not so good against others.

So how does this all tie up to you finding the love of your life? Currently, there are 2 possible theories:

Firstly, you may choose a partner on the basis of them having a very different genotype to your own. This would mean that your children will have a very diverse set of MHC molecules. This theory assumes that having the biggest diversity in MHC molecules will give people the best chance of surviving different illnesses.

This theory comes down to the ‘Red Queen’ theory (taken from a quote from Alice in Wonderland ‘it takes all the running you can do, to keep in the same place’), which says that every generation needs to keep evolving, changing, in order to be able to compete with other ever changing pathogens it encounters.

The second theory says that you choose a partner who has a particular genotype. For example, if a certain disease is in the population, it would be best to find a partner who is resistant to this disease, in order for your offspring to have the same resistance. This need would thus vary, depending on which disease is prevalent in the population at a given time. E.g., having a malaria protective MHC would be beneficial in malaria endemic countries, however, having a smallpox resistant gene doesn’t give much benefit these days.

However, this benefit only exists if the genotype is rare. If the genotype is common in the population, the pathogen will adapt to it and be able to evade the immune system. In contrast, if the genotype is rare, the pathogen will not adapt and the person will be protected.

Regardless of which theory is true, the question remains, how does a person determine both his/her own and their potential partner’s MHC set? You probably already guessed it from the title, it all comes down to smell.

It is thought that different MHC molecules emit different smells. This would make it possible for a female to smell which male offers the most suitable genes based on her own DNA. Several interesting (and sometimes disgusting) experiments were performed to support these theories.

In one of them, male participants were asked to wear the same t-shirt for several nights in a row. Afterwards, females were asked to smell these t-shirts and determine which ones were more attractive. In another, less nauseating experiment, participants were asked to rate different perfumes. This showed that people with the same MHCs had a preference for the same type of perfume.

So in short, you should be able to sniff out the love of your live.

Gwendoline Deslyper